159. "military sound". Is that what is offensive to you?

If you're talking about the POP of helicopter blades, here's what happens...

The tip of the blade that is traveling TOWARD you is breaking the sound barrier due to the forward speed of the propeller tip ADDED to the speed of the helicopter.

Once the helicopter PASSES you, the blade tip that's coming in your direction isn't breaking the sound barrier in relation to where you are because you have to SUBTRACT the speed the copter is traveling from the speed of the blade that's coming in YOUR direction. That's why the sound changes dramatically when the 'copter goes overhead.